With the popularization of computers in recent years, inkjet printers are widely used not only at offices but also at homes for printing letters or images on paper, films, cloths or the like.
The inkjet recording method includes a system of ejecting a liquid droplet upon applying a pressure by means of a piezoelectric element, a system of ejecting a liquid droplet by generating a bubble in an ink upon heat, a system of using an ultrasonic wave, and a system of ejecting a liquid droplet by drawing with an electrostatic force. An ink for use in such inkjet recording methods includes an aqueous ink, an oily ink and a solid (melt-type) ink. Of these inks, the aqueous ink becomes mainstream in view of production, handleability, odor, safety and the like.
A coloring agent used in such an ink for inkjet recording method is required to have high solubility in a solvent, enable high-density recording, have good color hue, exhibit excellent fastness to light, heat, air, ozone, water and chemicals, ensure good fixing property and less bleeding on an image-receiving material, provide an ink having excellent preservability, shows no toxicity, have high purity, and be available at a low cost. However, it is very difficult to find out a coloring agent satisfying these requirements at a high level. In particular, a coloring agent having good cyan color hue and excellent fastness to ozone is strongly desired.
Although various dyes and pigments for inkjet recording have been already proposed and practically used, a coloring agent satisfying all requirements is not yet found out at present. Conventionally well-known dyes and pigments such as those having a Colour Index (C.I.) number can hardly satisfy both color hue and fastness required to the ink for inkjet recording method.
The inventors have made technical searches for resolving the above-described problems in the inkjet ink using dye and found that an aqueous inkjet ink is many times particularly interior in image preservability due to water solubility of the dye. As dyes suitable for the aqueous inkjet ink, phthalocyanine dyes having specific structures are set forth in Patent Documents 1 to 3 described below. These techniques exhibit improvements in simultaneous pursuit of color hue and fastness. However, since the color hue and fastness are especially important characteristics together with ejection stability, further improvements have been desired.
Patent Document 1: JP-A-2003-3086 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)
Patent Document 2: JP-A-2003-3099
Patent Document 3: JP-A-2003-3109